Supercharging is a suitable means for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In any case, supercharging leads to an increase in volumetric power output and a more expedient power-to-weight ratio. If the swept volume is reduced, it is thus possible, given the same vehicle boundary conditions, to shift the load collective toward higher loads, at which the specific fuel consumption is lower.
Internal combustion engines may be supercharged by exhaust-gas turbocharging. The advantage of an exhaust-gas turbocharger for example in comparison with a mechanical charger is that no mechanical connection for transmitting power is required between the charger and internal combustion engine. While a mechanical charger extracts the energy required for driving it entirely from the internal combustion engine, and thereby reduces the output power and consequently adversely affects the efficiency, the exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases.
Supercharged internal combustion engines are preferably equipped with a charge-air cooling arrangement by means of which the compressed combustion air is cooled before it enters the cylinders. In this way, the density of the supplied charge air is increased further. In this way, the cooling likewise contributes to a compression and improved charging of the combustion chambers, that is to say to an improved volumetric efficiency. It may be advantageous for the charge-air cooler to be equipped with a bypass line in order to be able to bypass the charge-air cooler if required, for example after a cold start.
In the development of internal combustion engines, it is a basic aim to minimize fuel consumption, wherein the emphasis in the efforts being made is on obtaining an improved overall efficiency.
Fuel consumption and thus efficiency pose a problem in particular in the case of Otto-cycle engines, that is to say in the case of an applied-ignition internal combustion engine. The reason for this lies in the fundamental operating process of the Otto-cycle engine. Load control is generally carried out by means of a throttle flap provided in the intake system. By adjusting the throttle flap, the pressure of the inducted air downstream of the throttle flap can be reduced to a greater or lesser extent. The further the throttle flap is closed, that is to say the more the throttle flap blocks the intake system, the higher the pressure loss of the inducted air across the throttle flap, and the lower the pressure of the inducted air downstream of the throttle flap and upstream of the inlet into the at least three cylinders, that is to say combustion chambers. For a constant combustion chamber volume, it is possible in this way for the air mass, that is to say the quantity, to be set by means of the pressure of the inducted air. This also explains why quantity regulation has proven to be disadvantageous specifically in part-load operation, because low loads require a high degree of throttling and a pressure reduction in the intake system, as a result of which the charge exchange losses increase with decreasing load and increasing throttling.
To reduce the described losses, various strategies for dethrottling an applied-ignition internal combustion engine have been developed.
One approach to a solution for dethrottling the Otto-cycle engine is for example an Otto-cycle engine operating process with direct injection. The direct injection of the fuel is a suitable means for realizing a stratified combustion chamber charge. The direct injection of the fuel into the combustion chamber thus permits quality regulation in the Otto-cycle engine, within certain limits. The mixture formation takes place by the direct injection of the fuel into the cylinders or into the air situated in the cylinders, and not by external mixture formation, in which the fuel is introduced into the inducted air in the intake system.
Another option for optimizing the combustion process of an Otto-cycle engine consists in the use of an at least partially variable valve drive. By contrast to conventional valve drives, in which both the lift of the valves and the timing are invariable, these parameters which have an influence on the combustion process, and thus on fuel consumption, can be varied to a greater or lesser extent by variable valve drives. If the closing time of the inlet valve and the inlet valve lift can be varied, this alone makes throttling-free and thus loss-free load control possible. The mixture mass which flows into the combustion chamber during the intake process is then controlled not by a throttle flap but rather by the inlet valve lift and the opening duration of the inlet valve.
A further approach to a solution for dethrottling an Otto-cycle engine is offered by cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges. The efficiency of the Otto-cycle engine in part-load operation can be improved, that is to say increased, by a partial deactivation because the deactivation of one cylinder of a multi-cylinder internal combustion engine increases the load on the other cylinders, which remain in operation, if the engine power remains constant, such that the throttle flap may be opened further in order to introduce a greater air mass into the cylinders, whereby dethrottling of the internal combustion engine is attained overall. During the partial deactivation, the cylinders which are permanently in operation furthermore operate in the region of higher loads, at which the specific fuel consumption is lower. The load collective is shifted toward higher loads.
The cylinders which remain in operation during the partial deactivation furthermore exhibit improved mixture formation owing to the greater air mass or mixture mass supplied.
Further advantages with regard to efficiency are attained in that a deactivated cylinder, owing to the absence of combustion, does not generate any wall heat losses owing to heat transfer from the combustion gases to the combustion chamber walls.
Even though diesel engines, that is to say auto-ignition internal combustion engines, owing to the quality regulation on which they are based, exhibit greater efficiency, that is to say lower fuel consumption, than Otto-cycle engines in which the load—as described above—is adjusted by throttling or quantity regulation with regard to the charging of the cylinders, there is, even in the case of diesel engines, potential for improvement and a demand for improvement with regard to fuel consumption and efficiency.
One concept for reducing fuel consumption, also in the case of diesel engines, is cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges. The efficiency of the diesel engine in part-load operation can be improved, that is to say increased, by a partial deactivation, because, even in the case of the diesel engine, in the case of constant engine power the deactivation of at least one cylinder of a multi-cylinder internal combustion engine increases the load on the other cylinders still in operation, such that the cylinders operate in regions of higher loads, in which the specific fuel consumption is lower. The load collective in part-load operation of the diesel engine is shifted toward higher loads.
With regard to the wall heat losses, the same advantages are attained as in the case of the Otto-cycle engine, for which reason reference is made to the corresponding statements given.
In the case of diesel engines, the partial deactivation is also intended to prevent the fuel-air mixture from becoming too lean as part of the quality regulation in the event of decreasing load as a result of a reduction of the fuel quantity used.
The inventors herein have recognized that the multi-cylinder internal combustion engines with partial deactivation described in above, and the associated methods for operating the internal combustion engines, nevertheless have considerable potential for improvement, as will be explained briefly below on the basis of a diesel engine as an example.
In a direct-injection diesel engine, if, for the purpose of the partial deactivation, the fuel supply to the deactivatable cylinders is stopped, that is to say discontinued, the deactivated cylinders continue to participate in the charge exchange if the associated valve drive of the cylinders is not deactivated or cannot be deactivated. The charge exchange losses thus generated lessen, and counteract, the improvements achieved with regard to fuel consumption and efficiency by the partial deactivation, such that the benefit of the partial deactivation is at least partially lost, that is to say the partial deactivation in fact yields an altogether less pronounced improvement.
To remedy the disadvantageous effects described above, it may be expedient for switchable valve drives to be provided at the inlet side and at the outlet side, by which valve drives the deactivated cylinders are held closed, and thus no longer participate in the charge exchange, during the partial deactivation.
However, in the case of internal combustion engines supercharged by exhaust-gas turbocharging, switchable valve drives can lead to further problems because the turbine of an exhaust-gas turbocharger is configured for a certain exhaust-gas flow rate, and thus also for a certain number of cylinders. If the valve drive of a deactivated cylinder is deactivated, the overall mass flow through the cylinders of the internal combustion engine is reduced owing to the omission of the mass flow through the deactivated cylinders. The exhaust-gas mass flow conducted through the turbine decreases, and the turbine pressure ratio generally also decreases as a result. A decreasing turbine pressure ratio has the effect that the charge pressure ratio likewise decreases, that is to say the charge pressure falls, and only a small amount of charge air, or less charge air than intended, is supplied to the cylinders that remain operational. The small charge-air flow may also have the effect that the compressor operates beyond the surge limit.
Increasing again the overall mass flow conducted through the cylinders of the internal combustion engine during partial deactivation by virtue of the deactivated cylinders continuing to participate in the charge exchange is not expedient because the relatively cool charge air conducted through the deactivated cylinders considerably reduces the enthalpy of the exhaust-gas flow provided to the turbine. Here, it must be taken into consideration that the exhaust-gas enthalpy of the hot exhaust gases is determined significantly by the exhaust-gas pressure and the exhaust-gas temperature. The exhaust-gas mass is consequently not the only relevant aspect when considering the problem in question.
The effects described above lead to a restriction of the practicability of the partial deactivation, specifically to a restriction of the load range in which the partial deactivation can be used. A reduced charge-air flow rate that is supplied to the cylinders which are operational during the partial deactivation reduces the effectiveness or the quality of the combustion and has an adverse effect on the fuel consumption and pollutant emissions.
The charge pressure during partial deactivation, and thus the charge-air flow rate supplied to the cylinders that remain operational, could for example be increased by a small configuration of the turbine cross section and by simultaneous exhaust-gas blow-off, whereby the load range relevant for a partial deactivation would also be expanded again. This approach however has the disadvantage that the supercharging behavior is inadequate when all the cylinders are operated.
The charge pressure during partial deactivation, and thus the charge-air flow rate supplied to the cylinders that are still operational, could also be increased by virtue of the turbine being equipped with a variable turbine geometry, which permits an adaptation of the effective turbine cross section to the present exhaust-gas flow. The exhaust-gas back pressure in the exhaust-gas discharge system upstream of the turbine would then however simultaneously increase, leading in turn to higher charge-exchange losses in the cylinders that are still operational.
Accordingly, the inventors herein provide a method to at least partly address the above issues. In one example, a method for an engine having a first cylinder group and a second cylinder group includes responsive to engine operation in a first engine speed-load region, deactivating one or more cylinders of the second cylinder group, and responsive to the deactivating, adjusting exhaust valve timing of one or more cylinders of the first cylinder group. The method further includes responsive to engine operation a second engine speed-load region, adjusting exhaust valve timing of the one or more cylinders of the first cylinder group, and responsive to the adjusting, deactivating the one or more cylinders of the second cylinder group.
In another example, a supercharged internal combustion engine includes at least three cylinders, each cylinder having at least one outlet opening which is adjoined by an exhaust line for discharging exhaust gases via an exhaust-gas discharge system, each cylinder further having at least one inlet opening which is adjoined by an intake line for supply of charge air via an intake system, the at least three cylinders arranged into at least two groups with in each case at least one cylinder, each cylinder of a first group of the at least two groups being a cylinder which is in operation even in the event of partial deactivation of the internal combustion engine, and each cylinder of a second group of the at least two groups being formed as a load-dependently switchable cylinder, at least one outlet opening of at least one cylinder of the first group equipped with an at least partially variable valve drive, with an oscillating outlet valve which opens up or shuts off an associated outlet opening and which is adjustable at least with regard to a control time for opening, the oscillating outlet valve realizing a valve lift Δh1,ex between an open position and a closed position and opening up the associated outlet opening during an opening duration Δt1,ex. The internal combustion engine further includes an exhaust-gas turbocharger comprising a turbine arranged in the exhaust-gas discharge system and a compressor arranged in the intake system; an exhaust-gas recirculation arrangement, and a controller storing instructions that when executed cause the controller to, during a first condition, deactivate at least one cylinder of the second cylinder group, and responsive to the deactivation, adjust the at least partially variable valve drive to open the associated outlet opening relatively early.
In the internal combustion engine according to the disclosure, at least one outlet opening of a cylinder that is operational even during partial deactivation of the internal combustion engine is equipped with an at least partially variable valve drive, the outlet valve of which is adjustable at least with regard to the control time for opening.
This makes it possible, during the operation of the partially deactivated internal combustion engine, for the at least one adjustable outlet valve of the first cylinder group to be opened relatively early. By this measure, the temperature of the exhaust gas supplied to the turbine can be increased, such that exhaust gas of greater enthalpy is made available at the turbine inlet of the at least one exhaust-gas turbocharger.
A greater exhaust-gas enthalpy yields a higher turbine pressure ratio, and thus a higher charge pressure ratio, as a result of which more charge air can be or is supplied to the cylinders that remain operational during partial deactivation, specifically even if the deactivated cylinders no longer participate in the charge exchange and the mass flow through the internal combustion engine is greatly reduced. Surging of the compressor can be prevented. The load range in which the partial deactivation can be effectively used is expanded. The torque characteristic of the supercharged internal combustion engine during the partial deactivation is considerably improved.
If the at least one adjustable outlet valve is, during the partial deactivation, opened while combustion is still taking place, then during the course of the charge exchange of the first group, fuel-air mixture that is still in the process of combustion is discharged into the exhaust-gas discharge system, and the energy or heat bound in the fuel is released in the exhaust-gas discharge system, and thus close to the turbine. The effect which is intended according to the disclosure, and which is achieved, specifically that of increasing the exhaust-gas enthalpy, is then particularly pronounced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.